Over the past thirty years, the potential and observed dangers of heavy metal bearing materials and waste exposure to humans and the environment and the generation of nuisance odors and from solid waste management facilities has been the basis of extensive regulatory control. The leaching and transport of heavy metals into surface water bodies and groundwater is a grave concern because of the danger that the drinking water supplies and the environment will become contaminated. Heavy metal bearing materials and wastes, such products or waste, paint residues, sludge, plating wastes, sediments, foundry dusts, casting sands, steel mill dusts, shredder residues, wire insulation, refuse incinerator flyash, incinerator bottom ash, incinerator combined ash, scrubber residues from air pollution control devices such as cyclones, electrostatic precipitators and bag-house filter bags, may be deemed hazardous by the United States Environmental Protection Agency (U.S. EPA) pursuant to 40 C.F.R. Part 261 if containing certain soluble heavy metals above regulatory limits. Any solid waste can be defined as hazardous either because it is “listed” in 40 C.F.R., Part 261 Subpart D or because it exhibits one or more of the characteristics of a hazardous waste as defined at Part 261, Subpart C. These characteristics are: (1) ignitability, (2) corrosivity, (3) reactivity, and (4) toxicity as tested under the Toxicity Characteristic Leaching Procedure (TCLP). Heavy metal bearing materials and wastes can also be regulated under state and federal groundwater and surface water protection standards, which set total and leachable limits for heavy metals often lower than the TCLP criteria, as the wastes and materials are not in a lined landfill and exposed to direct groundwater, drinking water, storm waters and surface water bodies. The odor produced during management or stabilization of these wastes and materials, such as from refuse incinerator ash residues and operations that process ash residues, can become problematic for the operators of such facilities, as many waste generation and stabilization operations are nearby industrial, commercial and/or residential settings. Odor emissions are regulated mostly under local ordinance rules of nuisance and some countries under federal and/or state air quality regulations.
40 C.F.R., Part 261.24(a), contains a list of contaminants and their associated maximum allowable concentrations. The inorganic list includes As, Ag, Ba, Cd, Cr, Pb, Hg, and Se. If a contaminant exceeds its maximum allowable concentration, when tested using TCLP analysis as specified at 40 C.F.R. Part 261 Appendix 2, then the material is classified as hazardous. The TCLP test uses a dilute acetic acid either in de-ionized water (TCLP fluid 2) or in de-ionized water with a sodium hydroxide buffer (TCLP fluid 1). Both extracts attempt to simulate the leachate character from a decomposing trash landfill in which the hazardous waste being tested for is assumed to be disposed of in, and thus subject to the acetic acid leaching condition. Waste containing leachable heavy metals is currently classified as hazardous waste due to the toxicity characteristic, if the level of TCLP analysis is above 0.2 to 100 milligrams per liter (mg/L) or parts per millions (ppm) for defined metals. The TCLP test is designed to simulate a worst-case leaching situation, i.e., leachate which would typically be found in the interior of an actively degrading municipal landfill. Such landfills normally are slightly acidic with a pH of approximately 5+0.5. Countries outside of the US also use the TCLP test as a measure of leachability such as Taiwan, Philippines, Thailand, and Canada. Thailand also limits solubility of Cu and Zn, as these are metals of concern to Thailand groundwater. Switzerland and most European countries also regulate management of solid wastes by measuring heavy metals and salts as tested by a sequential leaching method using carbonated water simulating acid rainwater. Japan and the United Kingdom use similar carbonated DI water leach tests to measure for landfill leaching potential from heavy metals.
Additionally, U.S. EPA land disposal restrictions prohibit the land disposal of treated hazardous wastes that leach in excess of maximum allowable concentrations upon performance of the TCLP analysis. The land disposal regulations require that hazardous wastes are treated until the heavy metals do not leach at Universal Treatment Standard (UTS) levels from the solid waste at levels above the maximum allowable concentrations prior to placement in a surface impoundment, waste pile, landfill or other land disposal unit as defined in 40 C.F.R. 260.10.
Communities have local ordinances that regulate the generation of odors that would be a public nuisance, and in some cases regulators have established maximum allowable odor index levels. Maximum hourly average and daily average chemical gas and particulate levels have also been established under the US Clean Air Act and Amendments, and by OSHA and NIOSH. Odor Index Tests using varied levels of activated carbon mixed with the subject waste or material and utilizing a panel of people with human olfactory sense is one method of comparing odors. The panel is asked to confirm or deny sense of odor, which is related to the amount of activated carbon used in the subject waste and generates an odor index. The lower the index, the stronger the odor would be encountered. There may exist certain health and environmental release risks from the emission and transfer or diffusion of odor bearing gases, and thus the need to control and reduce such odiferous gases may extend beyond a simple nuisance issue. H2S gas for example, having a rotten egg odor, is highly toxic and can cause death in humans upon exposure to lower lethal levels at very low duration.
Leach tests subject solid wastes, including sludge, ash, residues, material or soil, to dilute acetic acid leaching (TCLP), buffered citric acid leaching (STLC), distilled water, synthetic rainwater (SPLP, MEP) or carbonated water leaching (Japanese, UK, Swiss, and USEPA SW-924). Synthetic rainwater leach tests are also often used to measure heavy metal solubility and compare such to groundwater and surface water state and federal standards where materials and wastes are either reused on-site or disposed in a manner other than lined landfills.
Suitable acetic acid leach tests include the USEPA SW-846 Manual described Toxicity Characteristic Leaching Procedure (TCLP) and Extraction Procedure Toxicity Test (EP Tox) now used in Canada. Briefly, in a TCLP test, 100 grams of waste are tumbled with 2000 ml of dilute and buffered acetic acid for 18 hours. The extract solution is made up from 5.7 ml of glacial acetic acid and 64.3 ml of 1.0 normal sodium hydroxide up to 1000 ml dilution with reagent water.
Suitable synthetic acid leach tests include the USEPA SW-846 Manual described Synthetic Precipitant Leaching Procedure (SPLP) and Multiple Extraction Procedure Test (MEP) now used in the US for sites where wastes are reused outside of leachate collected and lined landfills. Briefly, in a SPLP test, 100 grams of waste are tumbled with 2000 ml of dilute nitric and sulfuric acid for 18 hours. The extract solution is made up to pH at near 4.8 simulating acid rainwater East and West of the Mississippi. The MEP is the Multiple Extraction Procedure which uses the TCLP type test for the first extract and followed by 9 cycles of the SPLP, all of which report leachate values, and thus attempt to measure diffusion potential of the waste matrix.
Suitable carbonated water leach tests include the Japanese leach test which tumbles 50 grams of composited waste sample in 500 ml of water for 6 hours held at pH 5.8 to 6.3, followed by centrifuge and 0.45 micron filtration prior to analyses. Another suitable distilled water CO2 saturated method is the Swiss protocol using 100 grams of cemented waste at 1 cm3 in two (2) sequential water baths of 2000 ml. The concentration of heavy metals and salts are measured for each bath and averaged together before comparison to the Swiss criteria.
Suitable citric acid leach tests include the California Waste Extraction Test (WET), which is described in Title 22, Section 66700, “Environmental Health” of the California Health & Safety Code. Briefly, in a WET test, 50 grams of waste are tumbled in a 1000 ml tumbler with 500 grams of sodium citrate solution for a period of 48 hours. The heavy metal concentration is then analyzed by Inductively-Coupled Plasma (ICP) after filtration of a 100 ml aliquot from the tumbler through a 45 micron glass bead filter.
Suitable odor measure test would be include activated carbon modified samples with comparative olfactory measure of resultant odor by human panel.
Of specific interest and concern regarding the present invention is the leaching of individual heavy metal groups including As, Hg, Cd, Cr, Cu, and Pb and combinations thereof under TCLP, SPLP, MEP, CALWET, acid rainwater and acid rain derived surface water conditions and under regulatory tests which attempt to simulate dilute acid water leaching for determination of hazardousness of incinerator ash residues. In addition, the reduction of odor generation from the handling and stabilization of ash is desired, as the processing and stabilization of incinerator ash is often in close proximity to adjacent industrial, commercial and residential settings. In a specific case, incinerator ash management and stabilization caused strong odors which in turn resulted in complaints to regulators, and thus the subject invention was developed to reduce odors and allow for stabilization.
The present invention provides a method of reducing the leachability of material or waste including the groups As, Hg, Cd, Cr, Cu, and Pb and combinations thereof under TCLP, SPLP, MEP, CALWET, acid rainwater and acid rain derived surface water leaching conditions, and reduce sensible odors generated during such stabilization, with use of dilute acid semi-soluble DiCalcium Phosphate DiHydrate (DCPDH) [CaHPO4.2H2O] pulverized “seed” that minimize weight increase of the treated material or waste and permit immediate stabilized matrix management and handling without water application and mixing, without curing requirements and associated double handling required from interim storage piles, and while producing a free-flowing and more permeable stabilized material or waste suitable for excavator or loader loading, truck unloading and land disposal or immediate reuse spreading and compaction. The present invention recognizes the use of dilute acids as leaching fluids to which DCPDH will be added, and thus teaches use of a stabilizer that is dilute acid semi-soluble.
Unlike the present invention, prior art has taught stabilization of heavy metals by addition of water soluble or water based physical encapsulation agents, and have failed to recognize the value of stabilizers which are not water soluble or have limited water solubility, yet are semi-soluble or available in dilute acetic acid (TCLP), dilute sulfuric and nitric acid (SPLP/MEP) and dilute citric acid (CALWET), and failed to produce a stabilization process with reduction of odor production. In particular, O'Hara (U.S. Pat. No. 4,737,356) and Forrester (U.S. Pat. Nos. 5,245,114 and 5,430,233) teach the need to add water soluble phosphates to incinerator ash, auto shredder and wire insulation wastes, and incinerator bottom ash, which are at least 5 gm/100 ml water solubility, with the preferred embodiment being 100% water soluble phosphoric acid, and which increases the odors from incinerator ash. Prior art stabilization methods using Portland cement, lime, cement kiln dust, phosphoric acids, and combinations also produce a reduced permeability matrix or solid material form by adding water (by combination or as part of the water soluble agent addition) to the stabilization recipe for a chemical reaction which presents post-stabilization handling and disposal complications, whereas the present invention use of pulverized DCPDH acts to reduce metals solubility without significant reduction of waste permeability, without formation of cement-like non-free flowing material or waste, without curing time, without water hydration and associated material and waste weight increase, without double material and soil handling required for curing stockpiles, thus permitting immediate stabilizer material or waste handling, loading, disposal or reuse. The pulverized DCPDH semi-soluble seed stabilization method operates on the basic principle that sufficient wet dilute acid environment contact and mixing between the material or waste and DCPCH will occur within the TCLP, SPLP, MEP or CALWET extraction vessel. Although the exact reason for odor reduction is not know at this time, it is postulated that the odors are reduced due to the fine powder and neutral nature of DCPDH which acts as an adsorbent of organics and sulfides produced from ash. The extraction method(s) used to predict leaching potential all assume that field material or waste disposal conditions are subject to hydration by acid rainwater or acid leachate and involve some degree of interstitial mixing of heavy metals with the extract fluid over some minimal period of time in a saturated environment, and that such hydration can be simulated by an extract solute addition and mixing period. The DCPDH seed stabilization method thus utilizes the regulatory extraction procedure to allow for post-stabilized material or waste hydration, mixing and wet chemistry dilute acid environment contact between heavy metals and DCPDH. The extraction tests thus act as dilute acid stirred tank reactors, which provide the opportunity for heavy metals on the surface of materials and waste, and that which diffuses into the acid solution, to have ample opportunity to contact DCPDH seeds that also have surface active and/or soluble mineral formation potentials with the dilute acid soluble and/or available heavy metals. Studies by the inventor found that the lower surface area non-pulverized forms of DCPDH were less effective in reducing heavy metals solubility, which confirmed that the surface area and semi-solubility of the exposed surface area of DCPDH played an important role in the mineral formation potentials. One unique benefit of the dry seed technology is that SPLP, MEP, TCLP and CALWET extract fluid acid soluble and pulverized DCPDH can be applied to waste or material and dry mixed for uniformity in the field, and consequently test samples of such stabilizers are allowed to freely tumble or mix in the presence of the heavy metals in the extract solution for a given extraction period of time. This non-cemented and non-reacted acid semi-soluble DCPDH pulverized surface mixing greatly improves the wet environment substitution of heavy metals such as Pb, Cd, Cr, Ni, and As into calcium phosphate apatite surfaces. The extraction device effectively puts the heavy metals into solution as well as some DCPDH into solution and remaining DCPDH surfaces into wet contact and thus provides an excellent opportunity for surface substitution, sorption and precipitation of now solution soluble and solution face reactive heavy metals. Under this chemical mechanism, some or all stabilization agents are made available to the solution by the acid solution, and heavy metal ions are made available to the solution which in turn substitute and exchange for calcium on insoluble apatite surfaces and precipitate with stabilization agents in acid solution.
U.S. Pat. No. 5,202,033 describes an in-situ method for decreasing Pb TCLP leaching from solid waste using a combination of solid waste additives and additional pH controlling agents from the source of phosphate, carbonate, and sulfates.
U.S. Pat. No. 5,037,479 discloses a method for treating highly hazardous waste containing unacceptable levels of TCLP Pb such as lead by mixing the solid waste with a buffering agent selected from the group consisting of magnesium oxide, magnesium hydroxide, reactive calcium carbonates and reactive magnesium carbonates with an additional agent which is either an acid or salt containing an anion from the group consisting of Triple Superphosphate (TSP), ammonium phosphate, diammonium phosphate, phosphoric acid, boric acid and metallic iron.
U.S. Pat. No. 4,889,640 discloses a method and mixture from treating TCLP hazardous lead by mixing the solid waste with an agent selected from the group consisting of reactive calcium carbonate, reactive magnesium carbonate and reactive calcium magnesium carbonate.
U.S. Pat. No. 4,652,381 discloses a process for treating industrial wastewater contaminated with battery plant waste, such as sulfuric acid and heavy metals by treating the waste waster with calcium carbonate, calcium sulfate, calcium hydroxide to complete a separation of the heavy metals. However, this is not for use in a solid waste situation.
Unlike the present invention, however, none of the prior art solutions taught specific dilute acid semi-soluble dry pulverized DCPDH seed stabilization of heavy metal bearing material or waste containing one or more heavy metals while also forming a free-flowing, more permeable stabilized matrix suitable for loading, transport, disposal and reuse without having a cement-like reduced permeability and strength, and without the burden of curing and associated double waste handling, and without reduction of odor. Specifically, prior art has failed to teach the mechanism of acid semi-soluble and pulverized DCPDH seed to allow intentional leaching of heavy metals into the regulatory extraction vessel and subsequent substitution of such metals onto DCPDH surfaces and precipitation and complex formation with a certain acid semi-soluble amount of DCPDH in acid solution.